Quote:
Originally Posted by norm
Thanks All for your replies.
Hi John,
I noticed that Peter Read now makes a compact Truss Dob and if its based on the Obsession (15") I assume its going to be in the F4.2 range. I'm currently tossing up between a Tscope 14" @ f4.7-4.8 (kit form) or possibly the SDM compact - depending on its cost.
I may even bite the bullet on an SDM f15 @f4.8, which I probably could get away without a paracorr. The 2 eyepieces I currently have is a Pentax 10mm Xw and Panoptic 24mm.
Cheers, Norm
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Hi Norm,
I have actually used the first protype Peter Read built using his new ultra compact design. It was an 18"/F4.5 and funnily enough we had it side by side with an Obsession Ultra compact 18"/F4.2. Peters' scope had a Galaxy mirror and the Obsession had an OMI mirror. Both optics and scopes were superb.
Peters' ultra compact design copies a lot of ideas from the Obsession Ultracompact, which in itself copies a lot of ideas from John Hudek (Galaxy Optics) original compact design. Peter has also added some of his own design ideas and improvements, which IMO are excellent. Peters' design sacrifices a little bit of compactness in the interests of being a little more solid and rigid. I think Peters' design works the best. In addition to being a little more solid than the Obsession Ultracompact, Peters' scopes are an absolute work of art and a beautifully engineered and assembled product. I also preferred using the F4.5 focal ratio as opposed to the F4.2 focal ratio. Whilst both had Paracorrs the F4.5 scope offers a little bit better performance at EOF. The sacrifice there is that it is a little taller and you need a step ladder more often.
If you are going with a 15" scope, I would be inclined to order it at F4.5 as opposed to F4.2. This would still let you keep your feet on the ground. If going to 16" to 18" aperture you may prefer an F4.2 or F4.3 scope in the interests of keeping the eyepiece height as low as possible.
That aperture and quality of scope certainly warrants spending the money on a paracorr, if it is faster than F4.5. If you end up going with an F4.5 scope or slower, I would get the scope and try my eyepieces in it before ordering the paracorr. I have never felt a need to use the paracorr with my 10mm Pentax XW in the 18"/F4.5. The 24mm Panoptic may benefit from the paracorr at F4.5, but I would try it first.
Cheers,
John B